During the construction of a pipeline, and sometimes during the serviceable life of a pipeline, it is necessary to have the lines cleaned and pressure tested to ensure their safety, integrity and reliability. This is particularly true in the construction of pipelines used for the transportation of oil, gas and petroleum products.
Pipelines used in the petroleum industry vary greatly in size. Typical lines range from 4 inches in diameter to over 42 inches in diameter. They are constructed in both onshore and offshore locations. During the construction, before the pipelines can be used, they must be cleaned and tested. The lines are typically cleaned by washing out the lines with water and detergent and then inserting and forcing through the line an oversized pig or swab.
The compressible pigs are generally made of plastic, foam with smooth exterior surfaces, urethane, rubber or the like. Forcing the pig through the line by either air or hydraulic pressure cleans the line of accumulated unwanted debris left over during construction and locates buckled surfaces or dents in the line. If the pig is forced through the line under hydraulic pressure the air in the line is removed and the line is ready for pressure testing. Additional pigs are then inserted and forced through the line to remove the water after testing making the line ready for use.
The typical pig is generally cylindrical or bullet shaped and is generally 1" to 3" larger in diameter than the inside diameter or I.D. of the pipeline to be cleaned. A problem therefore exists in inserting the oversized pig into the lines in an efficient manner without damaging the pig. The more damage to the pig, the less efficient a cleaning device it becomes.
Conventional methods of inserting pigs or swabs on construction sites include compressing the pig to a narrow diameter by a series of clamps, freezing the pig while still clamped, removing the clamps, and inserting the frozen pig into the line. The freezing method requires that refrigeration equipment be available at the construction site which generally is in a remote area. Having sufficient refrigeration equipment available is a particular problem when larger size swabs are required for the swabbing of larger pipeline. Frozen pigs tend to break up as they are pushed through the line. Waiting until the pig thaws would help to eliminate this problem but, often because of hurried work demands a frozen pig is used. Further, freezing tends to deform the pig reducing its cleaning or squeezing properties.
Other methods used to insert pigs include pre-loading a testhead pipe with a pig in the pipe yard. This pre-loaded pipe is brought to the construction site for use. Problems still exist when more than one pig is required in a line. This requires additional pre-loaded test pipes and the additional time involved in removing and reattaching these pre-loaded pipes to the line.
Other means for inserting pigs include specially fabricated pig launchers for each size line. This requires use of an oversize pipe, a reducer, a flange at the pipeline riser end and a blind flange with a pig loading into close line and maintaining it under pressure. These custom-made launchers are expensive and need to be re-built for each particular job. This is due chiefly to the varying pipe sizes and gauges used in pipeline construction. Depending on the job a single pipe overall size can range from standard to double extra heavy. Flanges vary in size to accommodate the various grades of pipes being used.
Other devices for inserting cleaning pigs or balls have been proposed. These include the large sphere handling apparatus as described in U.S. Pat. No. 3,809,113 to Grove, et al which is permanently installed in pipelines for use during the operation phase. Other devices for inserting balls into pipelines during the operation phase have been proposed. These include U.S. Pat. No. 3,063,079 to Bergman, et al, which is a combination valve and cleaning ball launcher. Similar devices include pig ball injector U.S. Pat. No. 2,977,617 to Willis which is a combination pig ball injector and valve mechanism for inserting a cleaning ball while the line is flowing. These devices are incorporated in lines already in use and are flanged into the lines as part of the system.
Various pipeline scraper inserting devices have been employed. These include U.S. Pat. No. 2,575,146 to Thomas, U.S. Pat. No. 2,028,779 to Howe, et al and U.S. Pat. No. 1,006,261 to Mueller. The Thomas patent discloses an inserter for inserting a scraper of a size substantially less than the inside diameter of the pipeline. The Howe, et al patent relates to a device for inserting a mechanical scraper into the line without interrupting the flow of liquid through the line by means of a piston pulley and wench. The Mueller patent discloses forcing a mechanical cleaning device with compressible vane type members into a pipeline by means of a funnel shaped fitting. The Mueller device is sized to fit exactly within the inside diameter of the line to be cleaned. It cannot be used on lines of various wall thicknesses within a pipe diameter range. No means for firmly attaching the fitting to the pipeline are disclosed in the Mueller. Such means are necessary when forcing a compressible urethane pig into the line.
None of the listed inventions provide for the insertion of compressible polyurethane pigs into a pipeline during construction in a convenient, efficient and low cost manner. Consequently, a need exists for an improved method and apparatus for inserting pipeline pigs into a line during the construction phase which will result in greater efficiency, versatility and reliability, and reduce the time, expense and functional problems associated with the aforementioned conventional methods.